The present invention relates generally to ballast systems. More specifically, the present invention relates to bi-level output electronic ballast systems, particularly to bi-level output electronic high intensity discharge (HID) ballast systems.
Electronic ballasts regulate current or power using solid-state components rather than a magnetic core. Typical electronic ballasts operate lamps at high frequencies, which increases the efficacy of the lamps by 10 to 12%, compared with conventional 60-Hz operation using magnetic ballasts. For example, an electronic ballast operating two 40-W T12 lamps can use as little as 72 W total (an 18% reduction compared with an energy-efficient magnetic ballast), while reducing light output only slightly. In addition to the reduced power requirements, most electronic ballasts offer several other advantages over magnetic ballasts including: reduced flicker; reduced noise; reduced heat output; the ability to operate a plurality of lamps; and reduced weight. Some electronic ballasts also operate lamps at a reduced light output such as 75% of full light output, with a corresponding additional power reduction. Electronic ballasts that permit continuous dimming of fluorescent lamps to less than 1% of full light output also are known. Conventional electronic HID ballast systems offer similar advantages in terms of tight power regulation, small size, and low weight. However, such HID ballast systems typically do not include circuitry for performing a dimming function.
Dimming systems are known for other types of lamps, e.g., fluorescent lamp dimmers employ either a separate interface (0-10V or digital), toggling of the power line, phase control of the power line, or some type of line carrier communication. Such dimming systems are often employed to promote overall efficiency, i.e., energy savings, of the lighting system. Additional energy savings are also made possible by employing occupancy detectors in the lighting system. For example, U.S. Pat. No. 5,406,173 discloses a lighting control system including both occupancy detectors and light level detection circuitry which allows for various methods of light control using a single system.
It should also be noted that many of these known dimming systems are only compatible with specific types of occupancy sensor. It will be noted that type, as used herein, does not indicate the method of detecting occupancy, i.e., infrared or ultrasonic sensors, but rather the circuit parameters associated with the occupancy detector. For example, U.S. Pat. No. 5,130,613 discloses an occupancy detector compatible with 0-10V dimming systems which is not compatible with electronic HID ballast systems, since this type of sensor only provides a "low voltage" level output in the 0-10V range, while occupancy detectors comparable with electronic HID ballast systems switches the line voltage on and off.
U.S. Pat. No. 5,327,048 discloses circuitry which allows "bi-level dimming" of electromagnetic ballast systems. It accomplishes this by switching an additional reactive component into the low electromagnetic ballasting circuit. Moreover, the '048 patent discloses a circuit configuration whereby multiple occupancy sensors are connected to a common "control unit". However, these characteristics are not presently available in an electronic HID ballast system.
What is needed is a dimming system which is much simpler than most other conventional types of dimmers. Preferably, the bi-level output power HID electronic ballast system should be lower cost, i.e., it should be easily implemented with existing low cost occupancy sensors instead of specialized control circuitry. What is also needed is circuitry which advantageously permits the ballast to be easily configured for more than one lamp type, while concurrently reducing the number of ballasts a fixture manufacturer or sales channel has to stock. Additionally, in a system wherein a single, or multiple occupancy detectors can be employed a simplified control configuration would be beneficial.